Transition Metal Alkoxides. Preparation and Properties of Bis(aryloxo)iron(II) and Bis(alkoxo)iron(II) Complexes Having 2,2'-Bipyridine Ligands

Article abstract of DOI:10.1246/bcsj.53.673

A series of bis(aryloxo)iron(II), 2a-2g, and bis(alkoxo)iron(II), 2h-2k, complexes with 2,2'-bipyridine ligands (Fe()C6H4X)2(bpy)n and Fe(OR)2(bpy)n) have been prepared by the reactions of diethylbis(2,2'-bipyridine)iron(II) (1) with corresponding p-substituted phenols and alcohols, respectively. (X = NO2, CN, Cl, C6H5, H, and CH3; R = CH3, C2H5, iso-C3H7, and CH2C6H5).These compounds were characterized by IR and NMR spectroscopies and elemental analyses as well as by chemical reactions.Kinetic investigation of the reactions of 1 with phenols by a visible spectroscopic method supports a mechanism involving partial dissociation of the 2,2'-bipyridine ligand, followed by coordination of phenol and activation of the Fe-C2H5 bonds giving the bis(phenoxo)iron(II) compound.Thermolysis of bis(alkoxo)iron(II) complexes give not only disproportionation products of the alkoxo ligands (alcohols and aldehydes) but also organic products which are obtained as the result of C-O bond cleavage of the alkoxo groups.Interactions of 2 with acyl and alkyl halides lead to the formation of corresponding esters and ethers.Reactions of these iron(II) complexes with various organic acetates give corresponding acetates via an alkoxo exchange reaction.Bis(aryloxo)iron(II) complexes, 2, are hydrolyzed with H2O to yield phenols.Catalytic trans-esterification between ester and alcohol and Tishchenko type dimerization of benzaldehyde are effectively promoted under mild conditions by the bis(phenoxo)iron(II) and bis(benzyloxo)iron(II) complexes, respectively.